1. Field of the Invention
This invention relates to climate control apparatus and more specifically to providing multiple stages of supplemental heating in a climate control apparatus having at least two units of supplemental heat that operates in conjunction with an intelligent thermostat.
2. Description of the Prior Art
Both heat pump systems and air conditioning systems which can also function to provide heat to a conditioned space, may be provided with supplemental heating elements. Specifically, with respect to a conventional heat pump system, during operation in the heating mode, the outdoor heat exchange coil acts as an evaporator withdrawing heat from the surrounding environment, while the indoor heat exchange coil acts as a condenser, giving up heat to the surrounding air. The heated air is in turn provided to the comfort space by being blown thereto through a plenum. Because of the relative temperatures and volumes of air and refrigerant involved, the temperature of the air normally sent to the comfort zone, the leaving air temperature, is normally relatively low. In fact it is often insufficient to provide the heat needed to prevent occupant discomfort.
Thus, when ambient temperatures approach the lower ranges, supplemental or auxiliary heat is generally provided in the form of electric heating elements, in order to augment the low level of heat provided by the pump itself. When these supplemental heating elements are present, the thermostat will normally be able to issue calls for heat on two levels--one for the primary heat available from the heat pump itself, and the other for supplemental heat, normally provided by electric heating elements. If all the electric heating elements are energized upon a call for supplemental heat, however, a number of problems can occur. First the temperature of the air discharged into the comfort zone will suddenly become extremely hot. While generally not hazardous, the sudden gust of heat can be unpleasant for someone who is positioned near a vent, and can create generally uneven heat in the comfort zone. The uneven heat is not only physically unpleasant but can also result in the thermostat functioning improperly due to erroneous temperature sensing. In addition, because electric is generally the most expensive form of heating, being considerably more expensive than that provided by a heat pump, use of the entire electric heating capacity every time supplemental heat is called for is not an energy efficient means of heating a comfort space.
In the prior art, staged heating has been provided in order to avoid using the full panoply of electric heating units every time there is a call for supplemental heat. Thus, in U.S. Pat. No. 5,332,028 to Derrick A. Marris assigned to a common assignee, a heat pump system was provided with a plurality of units capable of furnishing supplemental heat, so that the amount of supplemental heat produced could be staged. This is also the case in U.S. Pat. No. 5,454,511 which is incorporated herein by reference and which teaches a programmable or "intelligent" thermostat that has the ability to generate a continuously varying `demand` signal. Intelligent thermostats are also described in U.S. Pat. No. 5,270,952 to Adams, U.S. Pat. No. 4,522,336 to Culp, U.S. Pat. Nos. 4,836,442, 4,702,413 and 4,702,305 to Beckey and U.S. Pat. No. 4,606,401 to Levine. The teachings of the U.S. Pat. No. 5,332,028, 5,270,952, 4,522,336, 4,836,442, 4,702,413, 4,702,305, and 4,606,401 and the 8171 application are herein incorporated by reference as they apply to a heat pump with supplemental heating units and to intelligent thermostats.
However in the prior art heat pumps, even with staged electric heating, the staging could not be fine tuned. The number of stages possible was equal to the number of independent electrical heating elements, generally one, two or three Thus, in order to achieve three different stages of heating, three independent elements had to be used, which meant three connections and three sets of control links. It is both simpler and less expensive to achieve the same degree of discrimination with fewer elements, or a higher degree of discrimination with the same number of elements. Furthermore, the staging of electric heat, especially as provided by the instant invention, can reduce the peak demand for electricity that effects the delivery of this utility by the provider thereof. This not only conserves energy, but also helps prevent brown-outs that may otherwise occur when the weather is unusually cold in a normally temperate climate.